Submarine slides in the fossil record

Increase and advances in sea-bottom investigation shed new light on the distribution and geometry of submarine landslides. Important aspects, such as morphology of top of bodies and scar zone and bottom geometry have been detailed revealed in several cases. The internal part of the bodies, the deformational and triggering mechanisms remain, however, still poorly known. On-land observation of fossil mass-wasting deposits may provide detailed information on 3D geometry and setting of bodies and on style and mechanism of internal deformation, which can be complementary to submarine, geophysical studies. Moreover, the presence of bodies of different age into the sedimentary record enables mass-wasting episodes to be studied in relationship with stratigraphic and sedimentological evolution of sedimentary basins. Comparison among different examples of on-land fossil mass-wasting deposits suggest that the smaller bodies are relatively easy to be defined and classified into one of the mass wasting processes (sliding-gliding, slumping, debris flows and avalanches, cohesive debris flows, ….). The largest bodies, the ones exceeding tens of kilometers of width and tens of meters of thickness, are always complex units, due to a multistory emplacement, often involving the entire spectra of mass wasting processes from block gliding to hyper-concentrated flows. They definitely prevail into the sedimentary record related to the evolution of active, contractional margins (accretionary wedges and collisional chains). Detachment of these bodies seems to have occurred by retrogressive failure of slope and front of the accretionary wedge, giving a mixing of blocks and slabs (olistoliths) differently deformed and of different age and provenance. Intrabasinal and extrabasinal rocks are often present in the same body, pointing out that such large bodies are the results of protracted instabilities of the wedge front-foredeep. Moreover, the complicate internal structure, the different origin of the component units, and the reconstructed multistory evolution suggest altogether that the emplacement of the large scale mass wasting complexes should not to be considered as a single, instantaneous process. Also considering limits and problems in comparing different scales and sizes, different geodynamical settings and compacted with non-compacted bodies, may the study of fossil mass wasting bodies give information not available from present-day submarine investigations? If yes, is this the only way for field geologists to contribute to recognition and mitigation of geo-hazards from submarine mass wasting? On the other hand, the comparison with present day examples is the only way to shed light on still unknown aspects of fossil mass wasting bodies.